Abstract P046: Interplay of Intronic and Promoter Region Polymorphisms Up-regulate Human Angiotensinogen and Cause Hypertension in Transgenic Mice
Angiotensinogen (AGT) is the substrate for the RAS-cascade and polymorphisms leading to its overexpression are linked to hypertension. We have shown that SNPs in linkage disequilibrium with -6A of the hAGT gene cause increased AGT expression and hypertension. Recently, two genome wide association studies (GWAS) have linked SNP at the +1164 in intron-I with increased blood pressure. The +1164A allele has stronger homology with HNF-3 binding site as compared to +1164G. HNF3 belongs to the family of “pioneer” transcription factors, which enable chromatin access for other tissue-specific transcription factors. Thus, we propose that a haplotype, where multiple SNP-groups occur together, is a better model to predict and study disease correlation with genetic variations than individual SNPs alone. Intronic SNPs could increase chromatin access thus modulating promoter-transcription factor (TF) interactions. To study these possible interactions between the intronic SNPs in the promoter and intron I of the hAGT gene, we have divided this gene in two major haplotypes: haplotype-I (containing -6A & +1164A) and II (containing -6G & +1164G). Reporter construct containing haplotype-I has increased promoter activity as compared to haplotype-II on transient transfection in human liver cells, without (hap-1: 73±2 vs. hap-II: 23.64±3.21 A.U; p<0.05) and with dexamethasone treatment (hap-1: 1174±68vs. hap-II: 333.3±37 A.U; p<0.05). Double transgenic mice (TG) containing human renin gene (hREN) and haplotype-I of the hAGT gene (containing 2.0 Kb of the promoter, all the introns, exons and 3’UTR of the hAGT gene at the HPRT locus) have increased basal and GR induced expression of the hAGT gene in liver, kidney and fat as compared to haplotype-II. Complementary CHIP analysis shows increased TF-chromatin binding in the liver of haplotype-I TG mice for HNF3β (4.35 folds), C/EBPβ (2.1 folds), STAT-3 (3.6 folds) and GR (4.2 folds). Crucially, haplotype-I TG mice have increased (p<0.05) SBP (137±4 mm Hg) when compared to haplotype-II mice (126±3 mm Hg). In conclusion, intronic SNPs regulate hAGT gene expression via complex interplay with SNPs in the gene-promoter and this underscores the need for a haplotype-based approach to genetic variability and disease correlation.
Author Disclosures: M. Kaw: None. B. Mopidevi: None. D.G. Kindell: None. N. Puri: None. A. Rana: None. S. Jain: None. A. Kumar: None.
- © 2015 by American Heart Association, Inc.